Estimate your Basal Metabolic Rate (BMR) and Total Daily Energy Expenditure (TDEE) to better plan your nutrition and fitness goals.
Male
Female
Sedentary (little or no exercise)
Lightly active (light exercise 1-3 days/week)
Moderately active (moderate exercise 3-5 days/week)
Very active (hard exercise 6-7 days/week)
Extra active (very hard exercise & physical job)
Basal Metabolic Rate (BMR)
Calories burned at complete rest
0 kcal
Total Daily Energy Expenditure (TDEE)
Calories burned based on activity
0 kcal
Understanding Your Metabolic Rate Results
When discussing metabolism, two primary numbers are crucial for understanding how your body utilizes energy:
Basal Metabolic Rate (BMR) and Total Daily Energy Expenditure (TDEE).
While clinical testing of metabolic rate involves indirect calorimetry (breathing into a machine to measure oxygen exchange),
mathematical formulas like the Mifflin-St Jeor equation used in this calculator provide a highly accurate estimation for the general population.
What is Basal Metabolic Rate (BMR)?
Your BMR represents the number of calories your body requires to perform the most basic life-sustaining functions
assuming you are at complete rest. This includes breathing, circulation, nutrient processing, and cell production.
Essentially, if you stayed in bed all day without moving, this is the energy your body would still burn.
BMR typically accounts for 60% to 75% of your total calorie burn.
What is Total Daily Energy Expenditure (TDEE)?
TDEE is the total number of calories you burn in a 24-hour period. It is calculated by taking your BMR and multiplying it
by an "Activity Factor" representing your physical activity level. This number is critical for weight management:
To Maintain Weight: Consume calories equal to your TDEE.
To Lose Weight: Create a caloric deficit (typically 500 calories below TDEE).
To Gain Muscle/Weight: Create a caloric surplus (typically 250-500 calories above TDEE).
Factors Influencing Metabolic Rate
Several variables impact your metabolic results:
Body Composition: Muscle tissue burns more calories at rest than fat tissue. Individuals with higher muscle mass generally have a higher BMR.
Age: Metabolism naturally slows as you age, often due to a loss of muscle tissue and hormonal changes.
Gender: Men typically have less body fat and more muscle mass than women of the same age and weight, resulting in a higher caloric burn.
Genetics: Some people naturally have a faster or slower metabolism, although lifestyle factors play a significantly larger role in total energy expenditure.
// Toggle between Imperial and Metric inputs
function toggleUnits() {
var radios = document.getElementsByName('units');
var selectedUnit;
for (var i = 0; i < radios.length; i++) {
if (radios[i].checked) {
selectedUnit = radios[i].value;
break;
}
}
var weightLabel = document.getElementById('weightLabel');
var heightImperial = document.getElementById('heightImperial');
var heightMetric = document.getElementById('heightMetric');
if (selectedUnit === 'imperial') {
weightLabel.innerText = "Weight (lbs)";
heightImperial.classList.remove('hidden');
heightMetric.classList.add('hidden');
} else {
weightLabel.innerText = "Weight (kg)";
heightImperial.classList.add('hidden');
heightMetric.classList.remove('hidden');
}
}
// Main Calculation Logic
function calculateMetabolicRate() {
// 1. Get Values
var gender = document.getElementById('gender').value;
var age = parseFloat(document.getElementById('age').value);
var weightInput = parseFloat(document.getElementById('weight').value);
var activityMultiplier = parseFloat(document.getElementById('activity').value);
var unitSystem = "";
// Determine unit system
var radios = document.getElementsByName('units');
for (var i = 0; i < radios.length; i++) {
if (radios[i].checked) {
unitSystem = radios[i].value;
break;
}
}
// 2. Validate Inputs
if (isNaN(age) || isNaN(weightInput) || isNaN(activityMultiplier)) {
alert("Please enter valid numbers for age and weight.");
return;
}
// 3. Normalize to Metric (Mifflin-St Jeor uses kg and cm)
var weightKg = 0;
var heightCm = 0;
if (unitSystem === 'imperial') {
// Convert lbs to kg
weightKg = weightInput / 2.20462;
// Get feet and inches
var feet = parseFloat(document.getElementById('feet').value);
var inches = parseFloat(document.getElementById('inches').value);
if (isNaN(feet)) feet = 0;
if (isNaN(inches)) inches = 0;
if (feet === 0 && inches === 0) {
alert("Please enter your height.");
return;
}
// Convert total inches to cm
var totalInches = (feet * 12) + inches;
heightCm = totalInches * 2.54;
} else {
// Metric
weightKg = weightInput;
heightCm = parseFloat(document.getElementById('cm').value);
if (isNaN(heightCm)) {
alert("Please enter your height in cm.");
return;
}
}
// 4. Calculate BMR (Mifflin-St Jeor Equation)
// Men: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
// Women: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161
var bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * age);
if (gender === 'male') {
bmr = bmr + 5;
} else {
bmr = bmr – 161;
}
// 5. Calculate TDEE
var tdee = bmr * activityMultiplier;
// 6. Display Results
var resultsArea = document.getElementById('resultsArea');
var bmrResult = document.getElementById('bmrResult');
var tdeeResult = document.getElementById('tdeeResult');
bmrResult.innerHTML = Math.round(bmr).toLocaleString() + " kcal/day";
tdeeResult.innerHTML = Math.round(tdee).toLocaleString() + " kcal/day";
resultsArea.style.display = "block";
}